(1) Field of the Invention
This invention relates to a photosensitive paper for electrophotography. More particularly, the invention relates to a photosensitive paper for electrophotography which is excellent in the blocking resistance, the adaptability to the paper feeding operation, the scratch resistance in the photosensitive layer and electric characteristics irrespective of humidity conditions in the operation atmosphere.
(2) Description of the Prior Art
Photosensitive papers broadly used for electrophotography comprise a paper substrate, an electrophotographic photosensitive layer formed on one surface of the substrate and an electrically conductive coating layer formed on the other surface of the substrate. For formation of the electrically conductive layer, there has been used a binder medium containing an inorganic or organic conducting agent incorporated therein (which will be hereinafter referred to as "electrically conductive binder medium"). As the conducting agent, there are used cationic, anionic and nonionic conductive resins, water-soluble inorganic salts, and water-soluble or moisture-absorbing, organic low-molecular-weight compounds. In each of these conventional electrically conductive binder media, a necessary electric conductivity is attained by maintaining an appropriate moisture content in the medium. Accordingly, photosensitive papers prepared by using these electrically conductive binder media have a very high moisture-absorbing property, and since also binder media per se are water-soluble, the blocking tendency (tacking phenomenon) is very conspicuous in the photosensitive papers. Further, the tendency of the photosensitive papers to curl becomes conspicuous when the humidity changes.
As means for eliminating the foregoing defects of photosensitive papers for electrophotography and providing good slip properties between photosensitive papers to improve the adaptability to the paper feed operation, there has been proposed and is known a method in which a slip improving agent is incorporated in an electrically conductive binder medium.
As typical instances of such slip improving agent, there can be mentioned white solid powders of talc, active clay, diatomaceous earth, silica, titanium dioxide and magnesia. However, if such white solid powder is incorporated into an electrically conductive binder medium in an amount sufficient to attain a significant improvement of the slip characteristic, electrophotographic photosensitive layers of the resulting photosensitive papers are readily scratched by frictional contacts between back and front surfaces of the piled photosensitive papers, especially by mutual friction at the paper feeding step, and if these scratches are formed, areas of the scratches are developed to cause contamination of the background. Further, the smoothness of the coated surface of the photosensitive paper is degraded because of the presence of a large quantity of the white solid powder. Still further, such white solid powder is very sensitive to the humidity and it has a property of adsorbing the moisture-absorbing substance contained in the electrically conductive binder medium. Accordingly, the slip characteristic changes depending on the change of the humidity, and the stability of the paper feeding operation is degraded. Still in addition, the electric conductivity of the electrically conductive coating layer of the photosensitive paper is drastically changed according to the change of the humidity, resulting in changes of various characteristics of a copied image.
As another type of the slip improving agent, there are known various waxes, higher fatty acids such as stearic acid and palmitic acid, derivatives of these higher fatty acids, olefin resins such as low-molecular-weight polyethylene and polypropylene, polyalkylene polyols such as high-molecular-weight polyethylene glycol, and silicones, and these organic slip improving agents have been incorporated in electrically conductive binder media such as mentioned above. However, these slip improving agents are still insufficient in preventing occurrence of the blocking (tacking) phenomenon among photosensitive papers, and especially under high humidity conditions, the efficiency of the paper feeding operation is reduced by the tacking phenomenon of photosensitive papers. Still further, in case of photosensitive papers prepared by using such slip improving agent, it is difficult to make air present between two piled photosensitive papers, and therefore, it is often difficult to feed photosensitive papers one by one smoothly and stably. Moreover, when such slip improving agent is employed, the surface smoothness is excessively heightened and there is caused a defect that such properties as the touch and graphic property are degraded.
As will readily be understood from the foregoing illustration, there has not been known a photosensitive paper for electrophotography which is satisfactory in all of the adaptability to the paper feeding operation, the scratch resistance of the photosensitive layer, the blocking resistance and electric characteristics.